1. Field of the Invention
The present invention relates to a strobe unit that is used while being connected to a camera which adopts a film or an imaging device as a recording medium, and a strobe unit control method.
2. Description of the Related Art
In general, strobe units include a chattering preventing unit connected to a flashing initiating unit. This is because the strobe unit is designed on the assumption that a camera including a mechanical synchro switch may be connected thereto. Specifically, if the synchro switch of a camera is a mechanical switch, chattering occurs for some time. A strobe unit that does not include the chattering preventing unit may erroneously initiate flashing a plurality of times. In order to prevent this kind of incident, the chattering preventing unit is included. Namely, when the synchro switch is turned on for the first time, the chattering preventing unit enables initiation of flashing. However, even if the on and off states of the synchro switch are repeated thereafter for a predetermined period of time, the chattering unit ignores the repeated switching of the on and off states. In general, cameras have the predetermined time set to 100 milliseconds.
In general, the predetermined time is called a chattering prevention time. Even when the mechanical synchro switch is adopted, if a high-performance mechanical synchro switch is employed despite a high cost, a chattering time during which chattering is under way can be shortened to 50 milliseconds or less. However, when a camera in which the chattering prevention time is set to 100 milliseconds is employed, an interval between flashings performed by a strobe unit during continuous photography is limited to a time permitting ten flashings per second in order to guarantee that the foregoing incident will not occur. The same applies to a case where a camera in which the chattering prevention time is set to 50 milliseconds or less is employed or a camera including a semiconductor synchro switch to be described below is employed. For the foregoing reason, the upper limit of the interval between emissions of flashlight during continuous flash photography is the time permitting ten flashlight emissions per second. Moreover, the camera including the semiconductor synchro switch has already been put on the market. Since the upper limit of the interval between flashings performed by a strobe unit is the time permitting ten flashings per second, even if a camera has the ability to perform flash photography ten or more times per second, the camera is designed to confine the number of times of flash photography to about ten times per second.
Aside from the foregoing strobe unit, devices including a chattering preventing facility are described in, for example, Japanese Utility Model application No. 2503522. For example, Japanese Utility Model Application No. 2503522 discloses a remote control unit using a xenon flash tube. In a case where the chattering preventing facility is implemented in the remote control unit, when a transmitter receives a signal via an X sync contact in a camera (equivalent to a mechanical synchro switch employed in an embodiment of the present invention), a chattering cancellation circuit cancels chattering. The transmitter transmits an optical pulsating signal to a flashing control circuit according to an output signal of the chattering cancellation circuit so as to cause the xenon flash tube to emit flashlights a plurality of times. A receiver receives the optical pulsating signal and controlled equipment connected to an output terminal of the receiver (equivalent to a strobe unit in accordance with the embodiment of the present invention) is activated. Moreover, the Japanese Utility Model Application No. 2503522 describes a case where the remote control unit is used as a relay. In this case, the output terminal of the receiver and the input terminal of the transmitter are linked by a cable. The receiver transfers a received optical pulsating signal to the flashing control circuit via bypass unit, which allows a signal to bypass the chattering cancellation circuit, by way of the output terminal, cable, and input terminal. This causes the flash tube to emit flashlight according to the received optical pulsating signal.
Namely, when the transmitter is connected to a camera, the chattering cancellation circuit is employed. When the remote control unit is used as the relay, the chattering cancellation circuit is bypassed. A user manually designates whether the chattering cancellation circuit is employed or bypassed.
In efforts to overcome the aforesaid drawback of the conventional strobe unit, namely, the drawback that when a strobe unit is designed to be connectable to both of a camera having a semiconductor synchro switch and a camera having a mechanical synchro switch, the upper limit of the interval between flashings is the time permitting about ten flashings per sec because of the inclusion of the chattering preventing unit, conceivably, whether the chattering cancellation circuit is used is manually designated as it is proposed in relation to the remote control unit.
Moreover, when a strobe unit is designed to be connectable to both cameras that have a mechanical synchro switch but are different from each other in a chattering time during which chattering is under way, what is conceived in order to overcome the drawback that the upper limit of the interval between flashings is the time permitting ten flashings per sec is to manually switch chattering cancellation circuits that are set to different chattering prevention times.
Namely, when a camera having a mechanical synchro switch is connected to a strobe unit, a chattering preventing unit is activated according to a chattering time during which chattering of the mechanical synchro switch is under way. When a camera having a semiconductor synchro switch is connected to the strobe unit, the chattering preventing unit is inactivated. Thus, whether the chattering preventing unit is activated may be manually designated.
However, when a user can freely switch the activation and inactivation of the chattering preventing unit, the user may find it annoying to switch the activation and inactivation. Moreover, there is a fear that the switching may be performed improperly. Flash photography may not be achieved in a desired manner. Furthermore, the inclusion of a switch for use in switching the activation and inactivation will discourage the efforts to compactly design a strobe unit or a camera at a low cost.